(CNN) -- Observers have been barred from a trial for two American journalists who were detained while covering the plight of North Korean defectors living along the China-North Korea border, a U.S. State Department spokesman said.

Ian Kelly told reporters that according to media reports, the trial began Thursday. He said the department was informed by the Swedish ambassador to North Korea that no observers are allowed in the courtroom.

Sweden represents the United States in North Korea, because the two countries, which fought on opposite sides during the three-year Korean War in the 1950s, do not have diplomatic relations.

Kelly called the trial an "opaque procedure."

He said the department was notified that the reporters have a defense attorney but wasn't given the lawyer's name. U.S. officials have repeatedly called for the journalists' release.

The journalists, Laura Ling and Euna Lee, were taken into custody March 17. They are reporters for California-based Current TV, a media venture of former U.S. Vice President Al Gore.

The idea of sending either him or New Mexico Gov. Bill Richardson to Pyongyang on a mission to get the journalists released has been floated to the North Koreans, senior administration officials told CNN.

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No answer has come so far, but the expectation is that once the trial is over the North will accept a visit by either Gore or Richardson to secure their release. Officials also believe that could jumpstart a dialogue with North Korea about returning to talks.

Richardson served as the U.S. ambassador to the United Nations and was energy secretary during the Clinton administration, and he has maintained contacts with North Korea. He took several trips there as ambassador, and he worked for the release of people held by the North Koreans in the past.

North Korea charged the reporters with illegal entry into the country, "hostile acts" and spying.

Analysts said the trial could be brief, and sentences might be handed down Thursday. The women could face years in labor camps if convicted.

Their families broke months of silence this week, making public pleas for their release.

"When the girls left the United States, they never intended to cross into North Korean soil. And if they did at any point, we apologize," Lisa Ling, Laura Ling's sister, said on "Anderson Cooper 360" on Wednesday.